Sydney Roosters will call on the best defence in the NRL and pile extra men into tackles in a bid to stop South Sydney's Damien Cook darting out of dummy-half in Saturday's grand final qualifier. Cook will hold the key to Souths' hopes in the grudge match at Allianz Stadium, having quickly developed into one of the key game breakers in the competition in 2018. According to figures from Fox Sports Stats, the Rabbitohs have won just two of seven games this year when Cook has run 75 metres or less, compared to 13 wins in the 17 matches he has topped that mark. That's a winning strike rate of 28 per cent when he doesn't reach 75 metres, as opposed to 76 per cent when he does. "It's really important (to stop him)," Roosters prop Sio Siua Taukeiaho told AAP. "He's one of the best hookers in the game and one of the best dummy-half runners when there is a quick play-the-ball. "We're more focused on slowing the ruck, that's what we're good at and what we do. That's what we've been practising through the whole pre-season. "Slow the ruck down, tackle as threes. If we can do that on the weekend then we should be able to look after Damien Cook." The Roosters, ranked No.1 in the regular season for defence, at least have form in doing that. The first time they played Souths this year, Cook was unstoppable. He ran 131 metres, had one linebreak, as linebreak-assist and five tackle busts in the Rabbitohs 26-14 round-six win to catapult himself into NSW State of Origin contention. Fast forward to round 22 when they met next, and it was a completely different story. The Roosters won the battle in the middle, controlled the Rabbitohs' ruck and restricted Cook to 58 metres. And in turn, the Tri-colours were triumphant 18-14. "We were more focused on tackling their middles, their forwards," Taukeiaho said. "They're the ones who get the quick play-the-balls for Damien Cook. "When we get all those sorted then that's when they get slow play-the-balls and he won't be able to get quick runs. "We spent that week focusing on our defence, our wrestle and our ruck play. "And on that week we were able to get that sorted and we were able to come out with the result. "And that's what we want (this week)." Australian Associated Press